Flexible grid optical spectrum transmitter, receiver, and transceiver

ABSTRACT

A coherent optical transmitter configured to generate a modulated optical signal within a portion of optical spectrum defined by a spectral position and spectral width, wherein the spectral width is ‘n’ bins where n is an integer greater than 1 and each bin is a same size, and wherein the spectral position and spectral width are specified by to the coherent optical transmitter via a management system.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present non-provisional patent application is a continuation of U.S.patent application Ser. No. 16/653,176, filed Oct. 15, 2019, andentitled “FLEXIBLE GRID OPTICAL SPECTRUM TRANSMITTER, RECEIVER, ANDTRANSCEIVER,” which is a continuation of U.S. patent application Ser.No. 15/411,456, filed Jan. 20, 2017 (now U.S. Pat. No. 10,461,880 whichissued on Oct. 29, 2019), and entitled “FLEXIBLE GRID OPTICAL SPECTRUMTRANSMITTER, RECEIVER, AND TRANSCEIVER,” which is a continuation-in-partof U.S. patent application Ser. No. 15/371,552, filed Dec. 7, 2016 (nowU.S. Pat. No. 10,200,145 which issued on Feb. 5, 2019), and entitled“FLEXIBLE GRID OPTICAL SPECTRUM TRANSMITTER, RECEIVER, AND TRANSCEIVER”and a continuation-in-part of U.S. patent application Ser. No.14/918,108, filed Oct. 20, 2015 (now U.S. Pat. No. 9,634,791 whichissued on Apr. 25, 2017), and entitled “FLEXIBLE OPTICAL SPECTRUMMANAGEMENT SYSTEMS AND METHODS,” which is a continuation of U.S. patentapplication Ser. No. 13/218,759, filed Aug. 26, 2011 (now U.S. Pat. No.9,197,354 which issued on Nov. 24, 2015), and entitled “CONCATENATEDOPTICAL SPECTRUM TRANSMISSION SYSTEM,” which claims priority to U.S.Provisional Patent Application Ser. No. 61/377,290, filed Aug. 26, 2010,and entitled “CONCATENATED OPTICAL SPECTRUM TRANSMISSION SYSTEM,” eachis incorporated in full by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to optical transmission systemsand methods. More particularly, the present invention relates toflexible optical spectrum transmission systems and methods that includea management system for provisioning and managing a flexible gridoptical spectrum transmitter, receiver, and transceiver which usesoptical spectrum through a plurality of bins.

BACKGROUND OF THE INVENTION

Fiber optic transmission systems and methods are widely recognized asthe most efficient way to transmit large amounts of data over longdistances. An important metric for these systems and methods is calledspectral efficiency. Spectral efficiency is a measure of the rate atwhich data can be transmitted in a given amount of optical spectrum,usually expressed in bits/s/Hz. The size of the available opticalspectrum is determined by factors such as the wavelength of lowattenuation in transmission fiber, bandwidth of optical amplifiers, andavailability of suitable semiconductor lasers and detectors. Forexample, the C-band may generally include optical spectrum of 1530-1565nm which corresponds to the amplification range and bandwidth oferbium-doped fiber amplifiers (EDFAs). Given that there is a finiteusable spectral range, the spectral occupancy and a given bit-rate ofthe channel, the spectral efficiency of a dense wave divisionmultiplexing (DWDM) system then determines the maximum informationcarrying capacity. As data demands increase, there is consistently aneed for more information carrying capacity given the finite constraintson the usable spectral range.

BRIEF SUMMARY OF THE INVENTION

In an exemplary embodiment, a flexible grid optical transmittercommunicatively coupled to an optical network includes a coherentoptical transmitter configured to generate a signal at a respectivecenter frequency on an optical spectrum and spanning n bins about therespective center frequency, wherein n is an integer greater than 1,wherein the respective center frequency and the n bins are utilized toperform Operations, Administration, Maintenance, and Provisioning(OAM&P) functions. The respective center frequency and the n bins can bespecified to the coherent optical transmitter by a management system forthe OAM&P functions. A value of n for the bins can be based on amodulation format and baud rate of a channel associated with the signal.Each of the n bins can include a same arbitrary size. The arbitrary sizecan be greater than or equal to 1 GHz and less than or equal to 12.5GHz. The arbitrary size can be selected based on physical parameters inthe optical network including any of roll offs, filter functions, sourcestability, and tunable laser performance in combination with applicationrequirements for channel size of the signal. The OAM&P functions caninclude managing the signal based in part on the respective centerfrequency and the n bins. The signal can have a spectral width, W_(i),that is less than or equal to n×a bin size of the n bins.

In another exemplary embodiment, a flexible grid optical receivercommunicatively coupled to an optical network includes a coherentoptical receiver configured to receive a signal at a respective centerfrequency on an optical spectrum and spanning n bins about therespective center frequency, wherein n is an integer greater than 1,wherein the respective center frequency and the n bins are utilized toperform Operations, Administration, Maintenance, and Provisioning(OAM&P) functions. The respective center frequency and the n bins can bespecified to the coherent optical receiver by a management system forthe OAM&P functions. A value of n for the bins can be based on amodulation format and baud rate of a channel associated with the signal.Each of the n bins can include a same arbitrary size. The arbitrary sizecan be greater than or equal to 1 GHz and less than or equal to 12.5GHz. The arbitrary size can be selected based on physical parameters inthe optical network including any of roll offs, filter functions, sourcestability, and tunable laser performance in combination with applicationrequirements for channel size of the signal. The OAM&P functions caninclude managing the signal based in part on the respective centerfrequency and the n bins. The signal can have a spectral width, W_(i),that is less than or equal to n×a bin size of the n bins.

In a further exemplary embodiment, a flexible grid optical transceivercommunicatively coupled to an optical network includes a coherentoptical transmitter configured to generate a transmit signal at arespective center frequency on an optical spectrum and spanning n binsabout the respective center frequency, wherein n is an integer greaterthan 1; and a coherent optical receiver configured to receive a receivesignal at the respective center frequency and spanning n bins about therespective center frequency, wherein the respective center frequency andthe n bins are utilized to perform Operations, Administration,Maintenance, and Provisioning (OAM&P) functions. The respective centerfrequency and the n bins can be specified to the coherent opticaltransmitter and the coherent optical receiver by a management system forthe OAM&P functions. A value of n for the bins can be based on amodulation format and baud rate of a channel associated with the signal.Each of the n bins can include a same arbitrary size. The arbitrary sizecan be greater than or equal to 1 GHz and less than or equal to 12.5GHz. The OAM&P functions can include managing the signal based in parton the respective center frequency and the n bins. The signal can have aspectral width, W_(i), that is less than or equal to n×a bin size of then bins.

In an exemplary embodiment, a flexible grid optical transmittercommunicatively coupled to an optical network includes a coherentoptical transmitter configured to generate a signal at a respectivefrequency/wavelength center and spanning a plurality of bins of opticalspectrum, wherein a size of each of the plurality of bins is based on arequired roll off of a wavelength selective component in the opticalnetwork. A number of the plurality of bins is based on a baud rate ofthe signal. The respective frequency/wavelength center and the pluralityof bins of optical spectrum can be provided to the coherent opticaltransmitter by a management system which manages the optical spectrum asflexible spectrum. The coherent optical transmitter can be tunable togenerate the signal at the respective frequency/wavelength center. Thecoherent optical transmitter can have a dynamic range wide enough togenerate the signal at any respective frequency/wavelength center in theoptical spectrum. The signal can utilize any of duo-binary, quadratureamplitude modulation (QAM), differential phase shift keying (DPSK),differential quadrature phase shift keying (DQPSK), orthogonalfrequency-division multiplexing (OFDM), and polarization multiplexingwith any of the foregoing.

In another exemplary embodiment, a flexible grid optical receivercommunicatively coupled to an optical network a coherent opticalreceiver configured to receive a signal at a respectivefrequency/wavelength center and spanning a plurality of bins of opticalspectrum, wherein a size of each of the plurality of bins is based on arequired roll off of a wavelength selective component in the opticalnetwork. A number of the plurality of bins is based on a baud rate ofthe signal. The respective frequency/wavelength center and the pluralityof bins of optical spectrum can be provided to the coherent opticalreceiver by a management system which manages the optical spectrum asflexible spectrum. The coherent optical receiver can be tunable toreceive the signal at the respective frequency/wavelength center. Thecoherent optical receiver can select the signal from the opticalspectrum while rejecting other signals present. The signal can utilizeany of duo-binary, quadrature amplitude modulation (QAM), differentialphase shift keying (DPSK), differential quadrature phase shift keying(DQPSK), orthogonal frequency-division multiplexing (OFDM), andpolarization multiplexing with any of the foregoing.

In a further exemplary embodiment, a flexible grid optical transceivercommunicatively coupled to an optical network includes a coherentoptical transmitter configured to generate a transmit signal at a firstfrequency/wavelength center and spanning a first plurality of bins ofoptical spectrum; and a coherent optical receiver configured to receivea receive signal at a second frequency/wavelength center and spanning asecond plurality of bins of optical spectrum, wherein a size of each ofthe first plurality of bins and the second plurality of bins is based ona required roll off of a wavelength selective component in the opticalnetwork. A number of the first plurality of bins and the secondplurality of bins is based on a baud rate of the transmit signal and thereceive signal, respectively. The first frequency/wavelength center, thesecond frequency/wavelength center, the first plurality of bins, and thesecond plurality of bins can be provided to the coherent opticaltransceiver by a management system which manages the optical spectrum asflexible spectrum. The coherent optical transmitter can be tunable togenerate the transmit signal at the first frequency/wavelength center.The coherent optical transmitter can have a dynamic range wide enough togenerate the signal at any frequency/wavelength center in the opticalspectrum. The coherent optical receiver can be tunable to receive thereceive signal at the respective frequency/wavelength center. Thecoherent optical receiver can select the receive signal from the opticalspectrum while rejecting other signals present. The signal can utilizeany of duo-binary, quadrature amplitude modulation (QAM), differentialphase shift keying (DPSK), differential quadrature phase shift keying(DQPSK), orthogonal frequency-division multiplexing (OFDM), andpolarization multiplexing with any of the foregoing.

In an exemplary embodiment, a flexible optical spectrum managementmethod in an optical network including a plurality of interconnectednetwork elements includes determining an associated frequency/wavelengthcenter and one or more bins for each of one or more traffic carryingchannels on optical fibers in the optical network; and managing the oneor more traffic carrying channels on the optical fibers using the one ormore bins of bins and the associated frequency/wavelength center,wherein at least one of the one or more traffic carrying channelsincludes a coherent optical signal occupying a flexible spectrum on theoptical fibers. A size of each of the one or more of bins can be smallerthan or equal to a smallest required roll off of a wavelength selectivecomponent in the optical network. A plurality of the one or more trafficcarrying channels can each be managed by concatenating a number of theone or more of bins together. Different baud rate channels are allocateda different number of bins. The method can be performed by one of anetwork management system (NMS), an element management system (EMS), anetwork controller, and a module in a network element. Each of aplurality of traffic carrying channels with a same A-Z path in theoptical network can be in a concatenated number of bins together withouta deadband between any of the plurality of traffic carrying channels. Aguardband can be configured using one or more bins for traffic carryingchannels with a different A-Z path in the optical network.

In another exemplary embodiment, a management system configured forflexible optical spectrum management in an optical network including aplurality of interconnected network elements includes a processorconfigured to determine an associated frequency/wavelength center andone or more bins for each of one or more traffic carrying channels onoptical fibers in the optical network, and manage the one or moretraffic carrying channels on the optical fibers using the one or morebins of bins and the associated frequency/wavelength center, wherein atleast one of the one or more traffic carrying channels includes acoherent optical signal occupying a flexible spectrum on the opticalfibers. A size of each of the one or more bins can be smaller than orequal to a smallest required roll off of a wavelength selectivecomponent in the optical network. A plurality of the one or more trafficcarrying channels can each be managed by concatenating a number of theone or more of bins together. Different baud rate channels are allocateda different number of bins. The management system can be one of anetwork management system (NMS), an element management system (EMS), anetwork controller, and a module in a network element. Each of aplurality of traffic carrying channels with a same A-Z path in theoptical network can be in a concatenated number of bins together withouta deadband between any of the plurality of traffic carrying channels. Aguardband can be configured using one or more bins for traffic carryingchannels with a different A-Z path in the optical network.

In a further exemplary embodiment, an optical network configured forflexible optical spectrum management includes a plurality of networkelements interconnected by optical fibers; and a management systemconfigured to determine an associated frequency/wavelength center andone or more bins for each of one or more traffic carrying channels onthe optical fibers in the optical network, and manage the one or moretraffic carrying channels on the optical fibers using the one or morebins of bins and the associated frequency/wavelength center, wherein atleast one of the one or more traffic carrying channels includes acoherent optical signal occupying a flexible spectrum on the opticalfibers. A size of each of the one or more bins can be smaller than orequal to a smallest required roll off of a wavelength selectivecomponent in the optical network. A plurality of the one or more trafficcarrying channels can each be managed by concatenating a number of theone or more bins together. Different baud rate channels are allocated adifferent number of bins. The management system can be one of a networkmanagement system (NMS), an element management system (EMS), a networkcontroller, and a module in a network element. Each of a plurality oftraffic carrying channels with a same A-Z path in the optical networkare in a concatenated number of bins together without a deadband betweenany of the plurality of traffic carrying channels, and wherein aguardband can be configured using one or more bins for traffic carryingchannels with a different A-Z path in the optical network.

In an exemplary embodiment, an optical network includes a first networkelement; a second network element communicatively coupled to the firstnetwork element by a first optical fiber; a first plurality of opticalchannels over the first optical fiber; and a second plurality of opticalchannels over the first optical fiber; wherein each of the firstplurality of optical channels are located on an optical spectrum withsubstantially no spectrum between adjacent channels, and wherein each ofthe second plurality of optical channels are located on the opticalspectrum with substantially no spectrum between adjacent channels. Aguardband may be defined on the optical spectrum between one end of thefirst plurality of optical channels and one end of the second pluralityof optical channels. The optical network may include a first flexiblespectrum wavelength selective switch at the second network element, thefirst flexible spectrum wavelength selective switch configured to dropthe first plurality of optical channels. The guardband may be spectrallydefined based on a roll-off associated with the first flexible spectrumwavelength selective switch. The optical network may further include, atthe second network element, a first power splitter coupled to a dropport of the first wavelength selective switch; and a first plurality ofCommon Mode Rejection Ratio (CMRR) coherent optical receivers coupled tothe power splitter, wherein each of the first plurality of CMRR coherentoptical receivers receives each of the first plurality of opticalchannels and selectively receives one of the first plurality of opticalchannels. The first flexible spectrum wavelength selective switch mayinclude a continuous spectral response on adjacent actuated portions ofthe optical spectrum when pointed to the same port.

The optical network may include a third network element communicativelycoupled to the second network element by a second optical fiber; whereinthe second plurality of optical channels is communicated over the secondoptical fiber and the first optical fiber. The optical network mayinclude a second flexible spectrum wavelength selective switch at thethird network element, the second flexible spectrum wavelength selectiveswitch configured to drop the second plurality of optical channels. Theoptical network may further include, at the third network element, asecond power splitter coupled to a drop port of the second flexiblespectrum wavelength selective switch; and a second plurality of CommonMode Rejection Ratio (CMRR) coherent optical receivers coupled to thepower splitter, wherein each of the second plurality of CMRR coherentoptical receivers receives each of the second plurality of opticalchannels and selectively receives one of the second plurality of opticalchannels. The optical network may include a plurality of bins defined onthe optical spectrum, wherein each of the first plurality of opticalchannels and each of the second plurality of optical channels areassigned to one or more of the plurality of bins. At least two of thefirst plurality of optical channels may include a different baud rate.

In another exemplary embodiment, an optical system includes a flexiblespectrum wavelength selective switch receiving a wavelength divisionmultiplexed (WDM) signal and including at least one drop port configuredto receive a first group of optical channels from the WDM signal withadjacent channels spectrally spaced substantially next to one another; apower splitter coupled to the at least one drop port; and a plurality ofCommon Mode Rejection Ratio (CMRR) coherent optical receivers coupled tothe power splitter, wherein each of the CMRR coherent optical receiversreceives each of the first group of optical channels and selectivelyreceives one of the first group of optical channels. The flexiblespectrum wavelength selective switch may include a continuous spectralresponse on adjacent actuated portions of an optical spectrum whenpointed to the at least one drop port. The flexible spectrum wavelengthselective switch may further include at least one express portconfigured to receive a second group of optical channels from the WDMsignal, wherein an optical spectrum of the WDM signal may include aguardband between the first group of optical channels and the secondgroup of optical channels. The guardband may be spectrally defined basedon a roll-off associated with the flexible spectrum wavelength selectiveswitch.

In yet another exemplary embodiment, a method includes defining aplurality of bins on an optical spectrum associated with an opticalfiber; dropping a first optical signal to a first coherent opticalreceiver, wherein the first optical signal uses one or more bins of theplurality of bins; and dropping a second optical signal to a secondcoherent optical receiver, wherein the second optical signal uses one ormore of adjacent bins to the one or more bins used by the first opticalsignal. The method may further include defining guardbands in one ormore of the plurality of bins, wherein the guardbands are spectrallydefined based on a roll-off associated with a flexible spectrumwavelength selective switch. A number of bins for each of the firstoptical signal and the second optical signal may be based on a formatand baud rate associated therewith. The method may further includeutilizing a management system to provision the first optical signal inthe one or more bins.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated and described herein with referenceto the various drawings of exemplary embodiments, in which likereference numbers denote like method steps and/or system components,respectively, and in which:

FIG. 1 is a spectral diagram of wavelength channel spacing constrainedby a demultiplexer filter response;

FIG. 2 is a table of an exemplary standard set of channels andfrequencies for optical spectrum from the InternationalTelecommunication Union (ITU);

FIG. 3 is diagram of an exemplary micro-electromechanical system(MEMS)-based wavelength-selective switch (WSS);

FIG. 4A is a drop section of an exemplary coherent augmented opticaladd/drop multiplexer (OADM);

FIG. 4B is an add section of the exemplary coherent augmented OADM;

FIG. 5 is a nodal configuration using the coherent augmented OADM forguardband minimization in concatenated optical spectrum transmissionsystems and methods;

FIG. 6 is a network diagram of an exemplary network of plurality ofoptical network elements configured with the nodal configuration of FIG.5;

FIG. 7 is a spectral diagram of wavelength channel spacing utilizing arange, group, or bin of channels for the concatenated optical spectrumtransmission systems and methods;

FIG. 8 is a spectral diagram of wavelength channel spacing utilizing abin of channels with a guardband contained within bins for theconcatenated optical spectrum transmission systems and methods;

FIG. 9 is a spectral diagram of an exemplary spectrum with three opticalchannels illustrated with different center frequencies and various bins;

FIG. 10 is a spectral diagram of another exemplary spectrum with variousoptical channels allocated thereon in a super channel with differentcenter frequencies and various bins; and

FIG. 11 is a flowchart of a process of assigning frequencies based onvarious selections, using FIG. 10 as an example.

DETAILED DESCRIPTION OF THE INVENTION

In various exemplary embodiments, the present disclosure relates toconcatenated optical spectrum transmission systems and methods thatallocate optical spectrum of groups of channels to reduce or eliminatedeadbands or guardbands (i.e., unused optical spectrum) betweenchannels. The concatenated optical spectrum transmission systems andmethods include various techniques for using optical spectrum such asover the C-band or any other frequency bands. In particular, theconcatenated optical spectrum transmission systems and methods provide abalance between fixed channel systems such as provided for by theInternational Telecommunication Union (ITU) and a more flexible systemenabled by coherent optical detection. In an exemplary embodiment, theconcatenated optical spectrum transmission systems and methods mayutilize a Wavelength Selective Switch (WSS) and a plurality of moderateCommon Mode Rejection Ratio (CMRR) coherent receivers in combination toachieve a concatenated optical spectrum.

Referring to FIG. 1, in an exemplary embodiment, a spectral diagram 10illustrates wavelength channel spacing constrained by a demultiplexerfilter frequency response 12. The spectral diagram 10 is a diagram ofoptical frequency versus transmission intensity, and the exemplaryspectral diagram 10 illustrates an optical channel. Prior to the adventof commercially available coherent optical transponders, all receiversrequired the DWDM system to filter out all but one optical channelbefore it was presented to a photodetector. Any practical filter has apassband shape response 12 which has a range of frequencies it can passefficiently, and then a gradual decrease in transmission efficiencyuntil the point where an acceptable isolation is achieved. For example,the shape response 12 shows an example shape which may be encountered insuch a system. The shape response 12 includes a passband portion 14 androll off portions 16. The limiting factor for channel spacing in thesesystems is the roll-off portions 16 of practical filters. In particular,the optical spectrum in the spectral diagram 10 may include variousfrequency portions including a useable channel passband 18 defined bythe passband portion 14, unusable spectrum 20 where the roll offportions 16 extends to a minimum receiver isolation level 22, and aclosest useable adjacent channel portion 24. The passband portion 14 maygenerally be referred to as having guardbands, i.e. the passband portion14 is spaced apart by the unusable spectrum 20 or guardbands. The bestway to overcome this waste of spectrum previously was to create filterswith a sharper roll off portion 16 thereby minimizing the unusablespectrum 20. Disadvantageously, such systems and methods introduce extracomplications and expense.

Referring to FIG. 2, in an exemplary embodiment, a table 30 illustratesan exemplary standard set of channels for optical spectrum. Inparticular, the table 30 is defined by the ITU and provides a standardset of channels offset by equal frequency spacing, e.g. 12.5 GHz, 25GHz, 50 GHz, and 100 GHz in the table 30. For example, thestandardization of optical spectrum are described in ITU-TRecommendation G.694.1 (06/2002) Spectral grids for WDM applications:DWDM frequency grid and ITU-T Recommendation G.698.2 (11/2009) Amplifiedmultichannel DWDM applications with single channel optical interfaces,the contents of each are incorporated by reference herein. The channelsin the table 30 are defined to provide an acceptable channel passbandsand guardbands. One advantage of standardizing channels is to allow acommon set of laser sources to be provided in the market. Anotheradvantage is to allow management systems to have a common way ofenumerating channels so as to keep track of them regardless of themanufacturer. In an exemplary embodiment, the concatenated opticalspectrum transmission systems and methods may utilize the channels inthe table 30 but in a modified fashion to adjust for applicationrequirements such as with coherent optical detection. The channelsillustrated in FIG. 2 are generally described as fixed grid spectrummanagement where each channel is fixed on the ITU-T frequency grid.

Referring to FIG. 3, in an exemplary embodiment, an exemplarymicro-electromechanical system (MEMS)-based wavelength-selective switch(WSS) 40 is illustrated. In this exemplary WSS 40, an input fiberincluding multiple wavelengths λ₁, λ₂, . . . λ₄, of optical signals isinput into a de-multiplexer 42, such as a diffraction grating or thelike. The de-multiplexer 42 separates each wavelength from the commoninput, and optionally a variable optical attenuator (VOA) 44 can beincluded following the de-multiplexer 42. VOAs 44 are configured toprovide variable attenuation to the wavelength, and the VOAs 44 can beremotely and dynamically set to a range of values. The WSS 40 includes apixel array 46 for each of the wavelengths λ₁, λ₂, . . . λ_(n). Thepixel array 46 includes a plurality of pixels per channel that deflectthe optical signal to an appropriate output port 48. Advantageously, theWSS 40 is fully reconfigurable for adding, dropping, and expressingthrough optical signals. Since there is the pixel array 46 for each ofthe optical signals, any signal can be dropped to any of the outputports 48. Additionally, multiple wavelengths including all wavelengthscan be dropped to a single port 48, such as an express port. To indicatedevice fan out, these WSS devices are often classified as “1×N” devices,e.g., a “1×9” WSS means a ten port device, with one common input andnine output ports.

The WSS 40 may be a flexible spectrum WSS which can switch and attenuateon arbitrary widths of spectrum based on the pixel array 46. Inparticular, the flexible spectrum WSS 40 is utilized in the concatenatedoptical spectrum transmission systems and methods to provide arbitraryspectral widths to avoid or reduce guardbands on optical spectrum. In anexemplary embodiment, the pixel array 46 may include a Liquid crystal onsilicon (LCOS) device with thousands of columns, pixels, etc. withhundreds of pixels per optical channel. In another exemplary embodiment,the pixel array 46 may include a Digital Light Processing (DLP)(available from Texas Instruments Inc.) device. Specifically, the pixelarray 46 may include any pixelated device which enables flexiblespectrum for each optical channel. For example, the flexible spectrumWSS 40 may include a granularity of 1 GHz or less per channel. The WSS40 can have a roll off of N GHz, such as N=12.5 GHz, 6.25 GHz, 4 GHz,etc. As technology evolves, the roll off of the WSS 40 has beendecreasing.

Referring to FIGS. 4A and 4B, in an exemplary embodiment, an exemplarycoherent augmented optical add/drop multiplexer (OADM) is illustratedwith a drop section 52 and an add section 54. In FIG. 4A, the dropsection 52 includes an n-channel Wavelength Division Multiplexed (WDM)signal 56 input to a drop section WSS 40 d having a set of p ports 58 (pbeing a positive integer), which are allocated between q (where q is aninteger greater than or equal to zero) express ports 58 e and m (where mis an integer an equal to p minus q) drop ports 58 d. The drop sectionWSS 40 d may include the WSS 40 in FIG. 3 or any other implementationthat is generally configured to route any given channel from the inputWDM signal 56 to any of the p ports 58 in a dynamic and reconfigurablemanner. Using the drop section WSS 40 d, a respective set of w (where wis an integer) wavelength channels from the WDM signal 56 may besupplied to each drop port 58 d. The number of wavelength channelssupplied to any given drop port 58 d may be the same, or different fromthe number of wavelength channels supplied to another one of the dropports 58 d.

A 1:s power splitter 60 (where s is an integer) may be connected to eachdrop port 58 d then supplies the respective set of channels to each oneof a corresponding set of s coherent optical receivers (cRx) 62. Thepower splitter 60 is configured to receive an output from each of thedrop ports 58 d and perform a splitting function providing a split copyof the output to s outputs. As described herein, the drop section WSS 40d may be a conventional WSS. In an exemplary embodiment, the WDM signal56 may be formatted to conform with a standard spectral grid, forexample an ITU-T grid having a 100 GHz channel spacing illustrated inthe table 30. In exemplary embodiments, the WDM signal 56 may havebetween n=32 and n=96 wavelength channels, and the WSS 40 d may havep=20 ports 48. The number (m) of drop ports 58 d, and the number (q) ofexpress ports 58 e may be selected as appropriate. For example, in amesh network node requiring eight-degree branching, a set of q=7 expressports 58 e is required, leaving m=13 ports available for use as dropports 58 d.

Each coherent receiver (cRx) 62 may be tunable, so that it can receive awavelength channel signal centered at a desired carrier wavelength (orfrequency). In an exemplary embodiment in which tunable coherentreceivers are used, the frequency range of each coherent receiver (cRx)62 may be wide enough to enable the coherent receiver (cRx) 62 to tunein any channel of the WDM signal 56. In other exemplary embodiments, thedynamic range of each coherent receiver (cRx) 62 may be wide enough toenable the coherent receiver (cRx) 62 to tune in anyone of a subset ofchannels of the WDM signal 56, such as w channels associated with theparticular drop port 58 d. With the arrangement of FIG. 4A, each of thecoherent receivers (cRx) 62 must be designed having a Common ModeRejection Ratio (CMRR) which enables the coherent receiver (cRx) 62 totune in and receive a selected one channel while rejecting each of theother s−1 channels presented to it by the power splitter 60. Becauses<n, the CMRR requirement for the coherent receivers (cRx) 62 issignificantly lower than that which would be required to support all nchannels. This relaxed CMRR requirement means that lower cost coherentreceivers may be used. However, it will be seen that, even with thelower CMRR of each coherent receiver 62, a total drop count of d=m*s isachieved. For example, consider a network system in which the WDM signal56 has n=96 wavelength channels, and the WSS 40 d has m=6 drop ports,each of which receives a respective set of s=16 channels. In this case,the total drop count is d=6*16=96 channels. In an exemplary embodiment,the coherent receiver 62 may be configured to support all of the nwavelengths. Here, the channels presented to the coherent receiver 62from the power splitter 60 do not have to be adjacent, but could bescattered anywhere across the n wavelengths. In another exemplaryembodiment, the coherent receiver 62 is configured to accept a subset ofthe n wavelengths, e.g. s wavelengths per receiver 62. In FIG. 4B, theadd section 54 of the coherent augmented OADM operates in a manner thatis effectively the reciprocal of the drop section 52 of FIG. 4B. Thus,an add section WSS 40 a is provided with a set of ports 58, which aredesignated as either add-ports 58 a or express ports 58 e. The addsection WSS 40 a operates to add the channels received through each port58 a into an outbound WDM signal 66 which is launched into a downstreamoptical fiber medium. Each express port 40 e receives a respective WDMoptical signal from upstream optical equipment such as, for example, thedrop section 52 of the same (or a different) OADM. Each add port 58 a isconnected to an s:1 power combiner 66 (where s is an integer) whichcombines the channel signals generated by a respective set of coherentoptical transmitters (cTx) 64. Some or all of the coherent opticaltransmitters (cTx) 64 connected to a given power combiner 66 may beoperating at any given time, so each add port 58 a will receive arespective set of w (where is an integer less than or equal to s)wavelength channels. The number of wavelength channels received by anygiven add port 58 a may be the same, or different from the number ofwavelength channels received by another one of the add ports 58 a. Withthis arrangement, the total number of transmitters that can be supportedis t=m*s. For example, consider a network system having a capacity ofn=96 wavelength channels, and the add section WSS 40 a has m=6 addports, each of which is coupled to a power combiner 66 that supports arespective set of s=16 transmitters. In a case where all of thetransmitters are generating a respective wavelength channel, each addport 58 a will receive a set of s=16 channels, and the total add countis t=6*16=96 channels.

In an exemplary embodiment, each coherent optical transmitter (cTx) 64is tunable so that it can selectively generate a wavelength channelsignal centered at a desired carrier wavelength (or frequency). Inexemplary embodiments in which tunable coherent optical transmitters(cTx) 64 are used, the dynamic range of each transmitter (cTx) 64 may bewide enough to enable the transmitter (cTx) 64 to generate any channelof the WDM signal 56. In other exemplary embodiments, the dynamic rangeof each transmitter (cTx) 64 may be wide enough to enable thetransmitter (cTx) 64 to generate anyone of a subset of channels of theWDM signal 56, such as one of s signals. The coherent optical receivers(cRx) 62 and the coherent optical transmitters (cTx) 64 may beconfigured to use any of duo-binary, quadrature amplitude modulation(QAM), differential phase shift keying (DPSK), differential quadraturephase shift keying (DQPSK), orthogonal frequency-division multiplexing(OFDM), polarization multiplexing with any of the foregoing, and anyother type of coherent optical modulation and detection technique. It isunderstood that for electronic channel discrimination, a tunable Rx isrequired. In nQAM and nPSK it is achieved using a linear receiver, i.e.a receiver where frequency mixing is taking place between a localoscillator and the incoming signal. The local oscillator needs to betuned at the right frequency such that the mixing product can be at baseband where all the necessary filtering will occur. If a receiver is notoperating like above, it requires a tunable optical filter prior to theoptical detector.

Generally, the WSS 40, 40 a, 40 d and other types of WSSs areessentially a polychrometer device with multiple output/input ports.Individual channels (i.e., wavelengths) can be switched by such a deviceand sharp roll-offs can be achieved. That is, the WSS 40, 40 a, 40 d maybe utilized to provide s demultiplexer function such as illustrated bythe demultiplexer filter shape response 12 in FIG. 1. The flexiblespectrum WSS 40, 40 a, 40 d can provide significantly improved roll-offportions 16 from other technologies such as arrayed waveguide gratings(AWGs) or thin film filters (TFFs). In an exemplary embodiment, theconcatenated optical spectrum transmission systems and methods mayutilize the coherent augmented OADM in FIG. 4 to eliminate individualchannel filtering at the drop ports 58 d. Thus, without thedemultiplexer, individual channels may be arranged or spaced closertogether only limited by the significantly improved roll-off portions 16associated with the WSS 40, 40 a, 40 d. Advantageously, through such aconfiguration, deadbands or guardbands may be reduced or eliminated. Thecoherent augmented OADM of FIGS. 4A and 4B may include additionalcomponents which are omitted for simplicity. For example, one ofordinary skill in the art will recognize that there may be opticalamplifiers added in these configurations to overcome the losses of WSS's40 a, 40 d and splitters 60, e.g. in location 58 d, and 58 a.

Referring to FIG. 5, in an exemplary embodiment, a nodal configuration70 illustrates guardband minimization in the concatenated opticalspectrum transmission systems and methods. The nodal configuration 70includes the drop section WSS 40 d and the add section WSS 40 aassociated with the coherent augmented OADM. To provide concatenatedoptical spectrum, the WSSs 40 a, 40 d provide a continuous spectralresponse on adjacent actuated portions of the spectrum when they arepointed to the same port 58. The selection of the number of these WSSs40 a, 40 d and their respective spectral widths is arbitrary and can bechosen according to system need and device design convenience. Anadvantage of the concatenated optical spectrum transmission systems andmethods is the ability to use the WSSs 40 a, 40 d which have roll-offswhich require small guardbands, but some portion of spectrum isconcatenated in such a way that there is no need for guardbands onadjacent channels within a sub-section of the spectrum.

The nodal configuration 70 receives a WDM signal 72 at an ingress pointand optionally may include an optical amplifier 74 to amplify thereceived WDM signal 72. The received WDM signal 72 includes a pluralityof channels (i.e. wavelengths) in a concatenated structure with respectto the optical spectrum. For example, the received WDM signal 72 mayinclude drop channels 76 and express channels 78 with a guardband 80therebetween. Specifically, each adjacent channel in the drop channels76 and the express channels 78 may abut adjacent channels with little orno spectral space therebetween. The only unused spectrum in the receivedWDM signal 72 may include the guardband 80. In terms of network-widefunctionality, the express channels 78 are configured to transit thenodal configuration 70 whereas the drop channels 76 are configured to bedropped and added at the nodal configuration 70. One of ordinary skillin the art will recognize the nodal configuration 70 may be repeated atother nodes in a network with the express channels 78 from theperspective of the nodal configuration 70 being drop channels 76 atanother node. Furthermore, this functionality of the nodal configuration70 applies as well to the coherent augmented OADM of FIGS. 4A and 4B.

The received and optionally amplified WDM signal 72 is input into a 1:zpower splitter 82 where z is an integer. For example, z may be thenumber of ports in the nodal configuration 70 with one port per degreeand one port for add/drop traffic. Alternatively, in a 1:2 mode, the 1:zpower splitter 82 may be omitted. The power splitter 82 is configured tosplit the WDM signal 72 in a plurality of copies on output connectionscoupled to a drop section WSS 40 d and an add section WSS 40 a. The dropsection WSS 40 d provides functionality similar to that described inFIG. 4A, namely there is no demultiplexer or filter in line to separatethe individual channels of the drop channels 76. Rather, a powersplitter 60 is configured to split the drop channels 76 into pluralcopies each of which is sent to coherent receivers (cRx) 62 which areconfigured with CMRR as described herein. In particular, the dropsection WSS 40 d is configured to perform a drop filtering function onthe drop channels 76 prior to the power splitter 60. In suchconfiguration with the CMRR coherent receivers (cRx) 62, the dropchannels 76 may be in a concatenated optical spectrum where there islittle or no guardbands between adjacent channels. Further, the CMRRcoherent receivers (cRx) 62 are configured to receive all of the dropchannels 76 and to selectively tune to a channel of interest.

The add section WSS 40 a is configured to receive the express channels78 from the power splitter 82 as well as local add traffic from coherenttransmitters (cTx) 64 (not shown in FIG. 5). The add section WSS 40 aincludes an output WDM signal 82 which includes the guardband 80 betweenadjacent concatenated spectrum portions. With respect to adding channelsin a concatenated fashion, the local add traffic may be added with thepower combiners 66. In another exemplary embodiment, the add section WSS40 a may have add ports 58 a for all local traffic, i.e. the WSS 40 amay be configured to multiplex the locally added channels together withlittle or no space therebetween in terms of optical spectrum. Forexample, The WSS 40 a may require a guardband for some isolation betweenthe channels due to limitations on the flexible spectrum WSS 40 a.Further, as WSS port count increases, it is also contemplated that theWSS 40 d may drop channels on an individual basis with each channelhaving little or no spectral space therebetween based on the fact thereis no need to provide isolation between ports on the WSS 40 d in theconcatenated optical spectrum transmission systems and methods describedherein. Those of ordinary skill in the art will recognize otherembodiments are also contemplated which generally will add channels insuch a manner as to not have spectral space therebetween. Further, thecoherent receivers 62 and the coherent transmitters 64 are illustratedas separate devices in FIG. 4, and those of ordinary skill in the artwill recognize these may be a single device referred to as a CMRRcoherent optical transceiver.

The concatenated optical spectrum transmission can also be referred toas flexible grid spectrum where the channels 76, 78, 82 can be locatedarbitrarily on the optical spectrum as opposed to the fixed gridspectrum where channels are assigned to a specific grid space withsignificant amounts of dead space and guard bands. Of note, the fixedgrid approach is operationally beneficial providing an efficientmanagement mechanism for operators, i.e., any transceiver can be managedby simply specifying the desired ITU grid slot. Of course, the fixedgrid approach is inflexible and inefficient especially with respect tocoherent modems which can use variable amounts of spectrum and do notrequire the guard bands between adjacent channels. Referring to FIG. 6,in an exemplary embodiment, a network 90 is illustrated of a pluralityof optical network elements 92 configured with the nodal configuration70 of FIG. 5. In this exemplary embodiment, the network elements 92 eachmay be configured to provide the concatenated optical spectrumtransmission systems and methods. The network elements 92 may includeany of WDM network elements, optical switches, cross-connects,multi-service provisioning platforms, routers, and the like with theCMRR coherent receivers (cRx) 62 and the coherent transmitters (cTx) 64.The network elements 92 are communicatively coupled therebetween byoptical fiber 94. For example, the network elements 92 are connected ina mesh architecture in the exemplary network 90, and those of ordinaryskill in the art will recognize the concatenated optical spectrumtransmission systems and methods are contemplated for use with anynetwork architecture, such as, for example, mesh, rings (BLSR, VLSR,UPSR, MS-SPRING, etc.), linear (1:1, 1+1, 1:N, 0:1, etc.), and the like.

The nodal architecture 70 at each of the network elements 92 isconfigured to transmit an optical spectrum 96 over the optical fibers94. In the network 90, in an exemplary embodiment, traffic generated atany network element 92 may terminate on another network element 92. Eventhough there are a large number of channels in the DWDM band, there is asmaller number of unique A-Z paths. The A-Z path includes an originatingnetwork element 92 and a terminating network element 92 with potentiallyintermediate network elements 92 where the channels are expressed. Atthe originating network element 92 and the terminating network element92, the channels in an A-Z path are added/dropped through the ports 58a, 58 d. At the intermediate network elements 92, the channels in theA-Z path are expressed. Using the concatenated optical spectrumtransmission systems and methods, the network 90 may be configured togroup A-Z demands together and place channels in the spectrum going onthe same path without deadbands between the channels in the same path.For example, the network 90 includes six network elements 92, and forfull connectivity between each network element 90, the optical spectrum96 may be segmented into five segments or groups 98. Within each group98, there is little or no unused spectrum, i.e. deadbands, using thenodal configuration 70. Between the groups 98, there is the guardband80. Specifically, the optical spectrum 96 is managed as flexible gridspectrum.

Referring to FIG. 7, in an exemplary embodiment, a spectral diagram 100illustrates wavelength channel spacing utilizing a range, group, or binof channels for the concatenated optical spectrum transmission systemsand methods. In an exemplary embodiment, the concatenated opticalspectrum transmission systems and methods may provide a completelyvariable spectrum where channels can be placed anywhere, i.e., theflexible grid spectrum. In this embodiment, to avoid the deadbands, A-Zdemands are placed in the same groups 90 in the spectrum. The spectraldiagram 100 introduces additional constraints to the selection ofspectral segments and the frequency range of channels for theconcatenated optical spectrum transmission systems and methods. Forexample, in the concatenated optical spectrum transmission systems andmethods, there are no requirements to define channels, frequencies,etc., but such a configuration is burdensome in operation for networkoperators, compared to fixed grid specrum. The aim of this approach isto constrain the channel placement in such a way as to ease the concernsof operators of such networks, i.e. to produce a set of channels whichis manageable similarly to the ITU grids which have become ubiquitous.However, this approach includes flexibility to account for theconcatenated optical spectrum transmission systems and methods.

In an exemplary embodiment, traffic carrying channels can be fixed tofrequency/wavelength centers which are defined by sub-grid elements.Alternatively, the traffic carrying channels can float within a bin 102.This would allow an optimization of performance of these channels usingarbitrary frequency spacing, while at the same time presenting a fixedrange of frequency for the bin 102 to the higher level management systemwhich is then un-encumbered of the exact frequency location of theoptical carriers, except to know that they are contained within the bin102.

In particular, the spectral diagram 100 illustrates an example of howconcatenated grids may work in the concatenated optical spectrumtransmission systems and methods. The spectral diagram 100 may besegmented into a plurality of bins 102 (i.e., groups, ranges, bands,etc.) of spectrum. Each of the bins 102 may occupy an equal amount ofspectrum similar or equivalent to the channels in table 30 of FIG. 2. Inan exemplary embodiment, each of the bins 102 may include a granularityof spectrum which is smaller than or equal to the width of the narrowestmodulated spectrum which is needed. This amount could be chosen, forinstance, to coincide with the smallest required roll off of the WSS 40and any other wavelength selective component used in the system.Further, one could also use devices which have a lower roll-off bysimply allocating multiple bins 102 to the filter guardband. Channelscan then be defined by concatenating a number of these bins 102together. If the bins 102 are enumerated, a descriptive and uniqueidentification may be generated by a channel in this system by statingthe start and stop bins 102, for example, channel 1-5 could mean thechannel which occupies bins 1 through 5 inclusive.

In the exemplary spectral diagram 100, six exemplary bins 102-1-102-6are illustrated. Those of ordinary skill in the art will recognize thatan optical spectrum may include any arbitrary number of bins 102. Thespectral diagram 100 includes a single group 98. A first bin 102-1 isoutside the group 98 and represents allocable spectrum for another group98 or channel. A second bin 102-2 is allocated as an unusable guardbandsuch as the guardband 80 in the nodal configuration 70. Bins 102-3,102-4, 102-5, 102-6 are all a part of the group 98. As described herein,channels within the group 98 do not require guardbands. Thus, in anexemplary embodiment, a coherent optical signal 104 may be provisionedin the bins 102-3, 102-4, 102-5, and the bin 102-6 may be useablespectrum for another coherent optical signal. In such a manner, thecoherent optical signals 104 may be provisioned on the spectral diagram100 with little or no unused spectrum.

In this manner, the specification of a center frequency and a number ofsmall sized bins 102 enables management of the flexible grid in a mannersimilar to fixed grid. This provides the benefits of the fixed grid froma management perspective while preserving the benefits of flex grid froma spectral efficiency perspective. As described herein, managementrefers to Operations, Administration, Maintenance, and Provisioning(OAM&P) functions in a network. For example, a management system cantrack and enable provisioning of transceivers for the management, usingthe center frequency and number of bins 102 thereabout to track thephysical location of the associated channel on the optical spectrum. Atransceiver can tune to the appropriate center frequency and use anamount of bandwidth based on the specified number of bins 102. That is,the specified center frequency and the number of bins 102 can be usedfor any OAM&P function by any device in an optical network.

Advantageously, the concatenated optical spectrum transmission systemsand methods provide a mechanism for minimizing deadband allocation. Theconcatenated optical spectrum transmission systems and methods furtherallows allocating varying widths of spectrum to individual channels suchthat one can optimize the amount of spectrum which is used. For example,a 10 Gbaud channel and a 40 Gbaud channel can be allocated differentnumbers of bins 102, a 100 Gbaud channel can be allocated yet anotherdifferent number of bins. For example, the concatenated optical spectrumtransmission systems and methods enable an optical transmission systemwith mixed baud rate channels without a loss of spectral efficiency. Ineffect, the bins 102 enable flexibility in the use of the opticalspectrum. That is, each channel may be provisioned to use only thespectrum it needs based on the associated modulation format.Advantageously, the concatenated optical spectrum transmission systemsand methods provide a fiber optic transmission system which groupschannels for the purpose of reducing or eliminating deadbands betweenchannels. The concatenated optical spectrum transmission systems andmethods further provides a fiber optic transmission system whichallocates spectrum on a predetermined group of bins to create virtualchannels with predictable start and end points in the optical spectrum.Furthermore, the concatenated optical spectrum transmission systems andmethods allow more efficient use of optical spectrum in an optical meshlike that in the network 90 by minimizing conflicts for spectrum, and byfixing the start and stop frequencies thereby allowing a simple methodto find a common set of sub-bins to bind together for a path from sourceto destination.

Referring to FIG. 8, in an exemplary embodiment, a spectral diagram 120illustrates wavelength channel spacing utilizing a bin of channels 102with a guardband contained within bins 102-2, 102-3 for the concatenatedoptical spectrum transmission systems and methods. The spectral diagram120 includes two coherent optical signals 122, 124. The optical signal122 occupies the bins 102-2, 102-3, 102-4, 102-5, 102-6 and the opticalsignal 124 occupies the bins 102-0, 102-1, 102-2. In this exemplaryembodiment, a guardband 126 is shared between the bins 102-2, 102-3.Specifically, the guardband 126 is contained within the bins 102-2,102-3, such that the bins 102-2, 102-3 start and end at nominally thesame frequency. The associated coherent receivers receiving the signals122, 124 may be configured as such and tune accordingly.

In an exemplary embodiment, the concatenated optical spectrumtransmission systems and methods may be implemented between the WSS 40,the coherent receivers 62, and a management system 85. The managementsystem 85 may include, for example, a network management system (NMS),an element management system (EMS), a network controller, a controlmodule or processor in a network element with the coherent receiver 62,and the like. In particular, the management system 85 may be configuredwith the plurality of bins 102 and associated optical signals 104, 122,124 configured thereon. The management system 85 variously may beutilized for OAM&P of an optical system. In performing suchfunctionality, the management system 85 may be utilized in theconcatenated optical spectrum transmission systems and methods to managethe bins 102 and respective optical signals thereon with the WSS 40, thecoherent receivers 62, etc.

Referring to FIG. 9, in an exemplary embodiment, a spectral diagram 200illustrates optical spectrum on an optical fiber with three exemplarychannels 202-1, 202-2, 202-3. Each of the channels 202-1, 202-2, 202-3has an associated center frequency 204-1, 204-2, 204-3 which representsa center of the channel 202-1, 202-2, 202-3 and is located in the middleof the bins 102. In an exemplary embodiment, the center frequency 204-1,204-2, 204-3 can be specified as a single value, such as a frequency(e.g., 195.8875 THz) or a wavelength (e.g., 1530.43 nm). In anotherexemplary embodiment, the center frequency 204-1, 204-2, 204-3 can bespecified as a frequency (or wavelength) value plus an offset value,e.g., center frequency=193.1 THz+n×bin size/2, where bin_size is thesize of the bins 102, in the same unit (here, in THz). In eitherapproach, a single value is used to specific the center frequency 204for OAM&P purposes, i.e., to communicate to the transceiver lasersettings, to track the optical spectrum by the management system 85,etc.

Each of the channels 202-1, 202-2, 202-3 in addition to the centerfrequencies 204-1, 204-2, 204-3 have a specified number of bins 102,greater than 1. If the number of bins 102 equaled 1, this would be thesame as the fixed grid approach, i.e., inefficient and inflexible. Thecenter frequency 204 is located at a center of the bins 102 for each ofthe channels 202-1, 202-2, 202-3. In the example where the number ofbins 102 is even, the center frequency 204 is located in a center of thebins 102 where a number of bins 102 to the left of the center frequency204 is equal to a number of bins 102 to the right of the centerfrequency 204. Here, left and right are logical constructs to visualizethe optical spectrum. In the example where the number of bins 102 isodd, the center frequency 204 is located in the middle of a center bin102 where the center bin 102 has an equal number of bins 102 to theright of it as to the left. Thus, to exactly determine the location ofany of the channels 202-1, 202-2, 202-3, only two values are requiredfor OAM&P purposes—the center frequency 204 and the number of bins 102.

In the example of FIG. 9, the channels 202-1, 202-2 are each shown with8 bins 102 whereas the channel 202-3 is shown with 32 bins. Assume thebin 102 size is 6.25 GHz, then the channels 202-1, 202-2 are 50 GHzchannels whereas the channel 202-3 is 200 GHz. Of course, otherembodiments are also contemplated. Of note, the center frequency 204 andnumber of bins 102 provide flexibility for flex grid systems—thechannels 202 can be placed anywhere, efficiently, without wastedspectrum, but also management efficient similar to the fixed gridapproach where two values—center frequency 204 and number of bins 102completely and precisely defines channel 202 location in the opticalspectrum for OAM&P functions. Again, as described herein, the OAM&Pfunctions can include, for example, using this data (center frequency204 and number of bins 102) by the transceiver to determine where totransmit a channel and over how much bandwidth, using this data by amanagement system 85 to track channels, manage the optical spectrum,determine a location for new channels, perform Routing and WavelengthAllocation (RWA) or Routing and Spectrum Allocation (RSA), and the like.

In an exemplary embodiment, the bin 102 size can be set to an arbitrary,but small value. By arbitrary, the bin 102 size is not tied to anyphysical parameters in the optical network (e.g., roll off, filterfunctions, laser centering errors, etc.). By small, the bin 102 size issmall, to provide flexibility for flex grid (e.g., bin_size≤12.5 GHz),but not too small (e.g., bin_size≥1 GHz) to provide operationallymeaningful values. For example, if the bin 102 size is greater than 12.5GHz, this value is similar to the fixed grid approach where the channel202 can cover an entire bin, thereby losing flexibility. If the bin 102is smaller than 1 GHz, this value increases operational complexity,requiring an extremely large number of bins 102. Thus, based ongranularity requirements for flexibility and operational concerns formanagement, the bin 102 size can arbitrarily set between 1≤bin_size≤12.5GHz.

In another exemplary embodiment, the bin 102 size is based on the rolloff requirements of wavelength selective components in the opticalnetwork. In this approach, the bin 102 size can be set to 12.5 GHz, 8GHz, 6.25 GHz, 4 GHz, etc. as required for roll off. Note, as theroll-off values become smaller with improved technology, it isadvantageous to decouple the bin 102 size from the roll off value asdescribed above for the arbitrary value since a small value for the bin102 size is not required for efficiency and granularity and also createscomplexity.

Those of ordinary skill in the art will recognize the bin 102 size inaddition to being arbitrarily selected based on application requirementsand being selected based on roll off values can also be selected basedon any other parameter of interest. For example, the bin 102 size can beselected based on frequency stability of laser sources in the networkwhich is typically on the order of 1-2 GHz, based on tunable laserperformance, and the like.

Also, the arbitrary range of between 1≤bin_size≤12.5 GHz is alsoselected generally based on these various physical parameters in general(roll-offs, filter functions, source stability, tunable laserperformance, etc.) in combination with a perspective of applicationrequirements. That is, greater than 12.5 GHz bin 102 size provideslittle advantage to the fixed grid approach, and less than 1 GHz bin 102size increases management complexity with no additional benefits inflexibility and efficiency. That is, a value in the single digits in allthat is needed based on transceivers and spectrum usage.

Advantageously, the use of the center frequency 204 and the number ofbins 102 provides OAM&P for flex grid in a manner similar to how fixedgrid approaches are managed today while preserving the benefits of theflex grid, allowing flexible channel spacing (no dead bands) andflexible channel size (variable number of bins 102). This paradigmallows network operators to use flex grid with similar OAM&P approachesused in the past with fixed grid approaches.

Referring to FIG. 10, in an exemplary embodiment, a spectral diagram ofanother exemplary spectrum 300 with various optical channels 302-1-302-5allocated thereon in a super channel with different center frequenciesand various bins. Again, as described herein, a flexible grid opticaltransmitter is tuned to a center frequency and provides a signal thatspans a number of bins (>1). FIG. 10 illustrates exemplary embodimentswhere the signal spans a partial number of bins 102 and the centerfrequency 204 of the transmitter is not necessarily aligned to thecenter of the selection of bins 102, i.e., the start and stopfrequencies of the signal are not aligned to the edges of the bins 102.That is, the selection of bins 102 can be wider in frequency than thesignal that is transmitted. This can be done in anticipation of i) othersignals being added to the same frequency range, e.g., a super channelor media channel, and ii) the current signal changing to a higher baudrate and/or different modulation format thereby increasing its frequencyusage.

Also, two or more transmitters can generate signals which transmitthrough a filter function defined by the center frequency and theselection of n bins (n is an integer greater than 1). This isillustrated, for example, in FIG. 10. Here, the five optical channels302-1-302-5 are located in 22 bins, and the channels 302-1-302-5 havewidths in GHz of 59.3, 51, 32.2, 58.3, and 48, respectively. The fiveoptical channels 302-1-302-5 can be in a super channel or media channelwhich can be a grouping of adjacent bins which are co-routed together inthe optical network between source and destination. Thus, the bins 102and center frequencies 204 can be used with individual channels orgrouping of channels.

Referring to FIG. 11, in an exemplary embodiment, a flowchartillustrates a process 400 of assigning frequencies based on variousselections, using FIG. 10 as an example. First, the process 400 includesstarting with (a) a selected bin size, e.g., 12.5 GHz or the like, (b) aset of flexible grid optical transceivers with known spectral widths,W_(i), and (c) filter properties of the transmission equipmentperforming the filtering function corresponding to the eventualselection of N bins (step 401). For the set of flexible grid opticaltransceivers, the known spectral widths are based on a given committedcapacity for each and an expected performance for the path in thenetwork. In the example of FIG. 10, the channels 302-1-302-5 have widthsin GHz of 59.3, 51, 32.2, 58.3, and 48, respectively. For thetransmission equipment, this is in the form of a filter deadband, whichis relatively constant in frequency and independent of the number ofselected bins to be concatenated. This is an inherent property of WSStechnology. These deadbands are usually symmetric, i.e., they are thesame size on both the lower and upper frequency edges of the resultingfilter, but they need not be. This corresponds to a lower deadband andan upper deadband. In FIG. 10, these deadbands are set at 6 GHz and 10GHz, respectively.

The process 400 includes determining the minimum required frequency asthe SUM(W_(i))+lower deadband+upper deadband (step 402). In this exampleof FIG. 10, the minimum required frequency is sum(59.3, 51, 32.2, 58.3,and 48)+6+10=264.8 GHz. The process 400 next includes determining thenumber of bins required, N=ceiling(minimum required frequency/bin size)(step 403). In this example of FIG. 10, the number of bins, N=22.

The process 400 next includes determining a portion of spectrum withenough free adjacent bins to fit N (step 404). This can involve Routingand Wavelength Assignment (RWA), Routing and Spectrum Assignment (RSA),or some other approach to find free spectrum for allocation. If thereare not enough adjacent bins, it may be necessary to split the set offlexible grid optical transceivers into smaller groups and return tostep 402. After step 404, the process can set the exact bins being used,including the start, stop and center frequency for the set of N bins.

The process 400 next include determining excess spectrum due to theceiling function in step 403, the excess spectrum=N*bin size−SUM(W_(i))(step 405). Here, the excess spectrum is due to the ceiling functionrounding up to the nearest whole number of bins, and the excess spectrumcan be allocated (step 406). In the example of FIG. 10, the excessspectrum=22*12.5−264.8 GHz=10.2 GHz. One approach to use this additionalspectrum is to place small guard bands between the transmitter signals.If they are each of equal size, than the excess guard band=excessspectrum/(# of transmitters−1). In the example of FIG. 10, this would be10.2/(5−1)=2.55 GHz. Using the additional spectrum in this way would bebeneficial in networks that are limited by crosstalk between thesignals, being either linear or nonlinear in nature. Another way to usethis excess spectrum would be to allocate it next to the deadbands. Thiswould be beneficial in networks with many filter locations, e.g., manyadd/drop nodes for example in a metro network.

Finally, the process 400 includes allocating a center frequency for eachof the set of flexible grid transceivers (step 407). This includesproviding commands to the flexible grid transceivers to tune inaccordance to their widths, deadbands and additional guard bands asneeded. In another embodiment, the known spectral widths, W_(i), of theset of flexible grid transceivers. above has additional guard bandsadded to them to minimize crosstalk penalties.

Thus, the transmitter widths, W_(i), are not constrained to be amultiple of the bin size and the deadbands are not constrained to be amultiple of the bin size.

In FIG. 10, the guardbands are shown between adjacent channels302-1-302-5 and the deadbands are shown at the beginning and end of thegrouping of channels 302-1-302-5. Of course, both guardbands anddeadbands are unused spectrum. As described herein, the guardbands anddeadbands can be less than the bin size. The guardbands can be zero orsome small value, as well as larger values to allow for future expansionof the channels 302-1-302-5. The deadbands can also be small values,allowing for wavelength selection.

It will be appreciated that some embodiments described herein, for themanagement system 85, may include one or more generic or specializedprocessors (“one or more processors”) such as microprocessors; CentralProcessing Units (CPUs); Digital Signal Processors (DSPs): customizedprocessors such as Network Processors (NPs) or Network Processing Units(NPUs), Graphics Processing Units (GPUs), or the like; FieldProgrammable Gate Arrays (FPGAs); and the like along with unique storedprogram instructions (including both software and firmware) for controlthereof to implement, in conjunction with certain non-processorcircuits, some, most, or all of the functions of the methods and/orsystems described herein. Alternatively, some or all functions may beimplemented by a state machine that has no stored program instructions,or in one or more Application-Specific Integrated Circuits (ASICs), inwhich each function or some combinations of certain of the functions areimplemented as custom logic or circuitry. Of course, a combination ofthe aforementioned approaches may be used. For some of the embodimentsdescribed herein, a corresponding device in hardware and optionally withsoftware, firmware, and a combination thereof can be referred to as“circuitry configured or adapted to,” “logic configured or adapted to,”etc. perform a set of operations, steps, methods, processes, algorithms,functions, techniques, etc. on digital and/or analog signals asdescribed herein for the various embodiments.

Moreover, some embodiments, for the management system 85, may include anon-transitory computer-readable storage medium having computer-readablecode stored thereon for programming a computer, server, appliance,device, processor, circuit, etc. each of which may include a processorto perform functions as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, an optical storage device, a magnetic storage device, a ROM(Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM(Erasable Programmable Read Only Memory), an EEPROM (ElectricallyErasable Programmable Read Only Memory), Flash memory, and the like.When stored in the non-transitory computer-readable medium, software caninclude instructions executable by a processor or device (e.g., any typeof programmable circuitry or logic) that, in response to such execution,cause a processor or the device to perform a set of operations, steps,methods, processes, algorithms, functions, techniques, etc. as describedherein for the various embodiments.

Although the present invention has been illustrated and described hereinwith reference to preferred embodiments and specific examples thereof,it will be readily apparent to those of ordinary skill in the art thatother embodiments and examples may perform similar functions and/orachieve like results. All such equivalent embodiments and examples arewithin the spirit and scope of the present invention and are intended tobe covered by the following claims.

What is claimed is:
 1. A coherent optical transmitter configured togenerate a modulated optical signal within a portion of optical spectrumdefined by a spectral position and spectral width, wherein the spectralwidth is ‘n’ bins where n is an integer greater than 1 and each bin is asame size, and wherein the spectral position and spectral width arespecified by to the coherent optical transmitter via a managementsystem.
 2. The coherent optical transmitter of claim 1, wherein themanagement system is one of a Network Management System (NMS), anElement Management System (EMS), a network controller, and a module in anetwork element.
 3. The coherent optical transmitter of claim 1, whereinthe spectral position and spectral width are specified by stating startand stop bins.
 4. The coherent optical transmitter of claim 1, whereinthe modulated optical signal has a spectral width that is less than nbins and determined at least by a baud rate of the modulated opticalsignal, to allow for insertion of at least one additional optical signalin the portion of the optical spectrum.
 5. The coherent opticaltransmitter of claim 1, wherein the coherent optical transmitter isconfigured to transmit the modulated optical signal down a path, alongwith one or more additional optical signals that also occupy the portionof the optical spectrum and are using the path.
 6. The coherent opticaltransmitter of claim 1, wherein a modulation format and a baud rate ofthe modulated optical signal is specified by the management system tothe coherent optical transmitter.
 7. The coherent optical transmitter ofclaim 1, wherein a size of each bin is smaller than a width of anarrowest modulated optical spectrum that is specified by the managementsystem.
 8. The coherent optical transmitter of claim 1, wherein a sizeof each bin is selected based on physical parameters including spectralcharacteristics of wavelength selective components.
 9. The coherentoptical transmitter of claim 1, wherein a size of each bin is equal to asmallest roll off of a wavelength selective component in a path.
 10. Thecoherent optical transmitter of claim 1, wherein a size of each bin is6.25 GHz.
 11. The coherent optical transmitter of claim 1, wherein asize of each bin is greater than or equal to 1 GHz and less than orequal to 12.5 GHz.
 12. The coherent optical transmitter of claim 1,wherein the modulated optical signal and one or more additional opticalsignals are located within the portion of optical spectrum with no deadband in between.
 13. The coherent optical transmitter of claim 1,wherein the modulated optical signal and one or more additional opticalsignals located within the portion of optical spectrum are separatedspectrally by at least one bin from other optical signals having adifferent path.
 14. The coherent optical transmitter of claim 1, whereinthe modulated optical signal and one or more additional optical signalsfloat even within a bin, thus allowing arbitrary frequency spacingtherebetween.
 15. The coherent optical transmitter of claim 1, whereinthe modulated optical signal and one or more additional optical signalsare switched together at an end of a path by a wavelength selectivecomponent to a common port, and the modulated optical signal isdemodulated by a coherent receiver configured to reject the one or moreadditional optical signals received from the common port.
 16. Thecoherent optical transmitter of claim 15, wherein the modulated opticalsignal and the one or more additional optical signals are identical inmodulation format and baud rate.
 17. The coherent optical transmitter ofclaim 15, wherein the modulated optical signal and the one or moreadditional optical signals vary in the number of bins each occupy. 18.The coherent optical transmitter of claim 1, wherein the coherentoptical transmitter has a dynamic range wide enough to generate themodulated optical signal anywhere within at least the portion of theoptical spectrum.
 19. A coherent optical receiver configured to receiveand demodulate a modulated optical signal within a portion of opticalspectrum defined by a spectral position and spectral width, wherein thespectral width is ‘n’ bins where n is an integer greater than 1 and eachbin is a same size, and wherein the spectral position and spectral widthare specified to the coherent optical receiver by a management system.20. The coherent optical receiver of claim 19, wherein the coherentoptical receiver has a dynamic range wide enough to tune anywhere withinat least the portion of the optical spectrum to demodulate the modulatedoptical signal, while rejecting any other optical signals within theportion of optical spectrum.
 21. A Wavelength Selective Switchconfigured to provide a passband in a portion of optical spectrumdefined by a spectral position and spectral width, wherein the spectralwidth is ‘n’ bins where n is an integer greater than 1 and each bin is asame size, and wherein the spectral position and spectral width arespecified by to the Wavelength Selective Switch via a management system.22. The Wavelength Selective Switch of claim 21, wherein the managementsystem is one of a Network Management System (NMS), an ElementManagement System (EMS), a network controller, and a module in a networkelement.